Recently, compact mobile devices are put to practical use toward the realization of a ubiquitous society, and demands for a compact, large-capacity, nonvolatile memory have been rapidly increasing year by year with the spread of the compact mobile devices. Among the various types of memory, the recording densities of NAND type flash memory and compact HDD (Hard Disk Drive) are rapidly being enhanced in response to the growing market.
However, in both the NAND type flash memory and the compact HDD, a problem of a limit of the recording density will be generated in the near future. Particularly, a limit of tracking accuracy relates to the compact HDD, and an increase of a process cost is generated due to a limit of microfabrication and reduction of a minimum line width in the NAND type flash memory. There is a strong demand for technological development of overcoming the limit of the recording density, and a novel solid-state memory has been proposed in order to considerably exceed the limit of recording density.
Conventionally, a memory in which an ON state (amorphous state) and an OFF state (crystalline state) are used by changing a film state (an amorphous state and a crystalline state) of a recording material called a PRAM (Phase change RAM) is proposed as a novel solid-state memory, and has been developed and is close to practical use (for example, see T. Gotoh et al., Jpn. J. Appl. Phys., 43, 6B, 2004, L818 and A. Sawa, T. Fuji, M. Kawasaki and Y. Tokura, Appl. Phys, Lett., 85, 18, 4073 (2004)).
Recently, research and development of the novel solid-state memory called a RRAM (Resistive RAM) have been promoted, and recording materials such as NiO and CuO are reported. In the RRAM, a voltage pulse is applied to the recording material, a low-resistance state (setting state) and a high-resistance state (resetting state) are repeatedly changed by utilizing a change in resistance of the recording material, and the state is converted into binary data (0 or 1) to record or erase information. One of the features of the RRAM is that the RRAM can be operated in principle even if an element size is reduced to about 10 nm. Because the RRAM can realize a recording density of about 10 Tbpsi (terabytes per square inch), the RRAM is a potential candidate for high recording density.
There is also proposed a MEMS memory in which a MEMS (Microel Ectro Mechanical System) technology is used (for example, see P. Vettiger, G. Cross, M. Despont, U. Drechsler, U. Durig, B. Gotsmann, W. Haberle, M. A. Lants, H. E. Rothuizen, R. Stutz and G. K. Binnig, IEEE Trans. Nanotechnology 1, 39 (2002)). In the MEMS memory, because an interconnection is not required in a recording portion, an extremely high recording density can possibly be realized. Recently, a combination of the MEMS technology and various recording principles has been proposed to study power consumption, recording and reproducing density, and operation speed (for example, see P. Vettiger et al. in Technical Digest, IEDM03 pp. 763-766). However, the novel information recording medium utilizing the resistance-change type recording material mentioned above has not currently been realized. This is attributed to the following facts. That is, the novel information recording medium is largely degraded by repetition of memory switching, thermal stability is low in each resistance state, and a problem of a heat resistance property (process resistance property) of a recording layer/electrode layer is generated by a post-annealing treatment.